The sphingosine-1-phosphate (S1P) receptors 1-5 constitute a family of G protein-coupled receptors with a seven-transmembrane domain. These receptors, referred to as S1P1 to S1P5 (formerly termed endothelial differentiation gene (EDG) receptor-1, -5, -3, -6, and -8, respectively; Chun et. al., Pharmacological Reviews, 54:265-269, 2002), are activated via binding by sphingosine-1-phosphate, which is produced by the sphingosine kinase-catalyzed phosphorylation of sphingosine. S1P1, S1P4, and S1P5 receptors activate Gi but not Gq, whereas S1P2 and S1P3 receptors activate both Gi and Gq. The S1P3 receptor, but not the S1P1 receptor, responds to an agonist with an increase in intracellular calcium.
The compound (R)-2-(7-(4-cyclopentyl-3-(trifluoromethyl)benzyloxy)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl)acetic acid (Compound 1) is a potent (EC50 cAMP, 0.093 nM (human)) and selective (EC50 β-arrestin, 6.10 nM (S1P1), >10,000 nM (S1P2), >10,000 nM, (S1P3), 147 nM (S1P4), and 24.4 nM (S1P5)), orally available investigational drug candidate for the S1P1 receptor.
In preclinical studies, Compound 1 showed calculated lymphocyte lowering IC50 values in four different species: 0.101 μM (mouse), 0.051 μM (rat), 0.058 μM (dog), and 0.098 μM (monkey). Notably, the calculated lymphocyte lowering IC50 values reflect total plasma concentration wherein Compound 1 is highly protein bound (97.8% human, 98.0% rat). Compound 1 was shown to be efficacious in the murine experimental autoimmune encephalomyelitis (EAE) model that mimics multiple sclerosis. Prophylactically, Compound 1 prevented the onset and severity of disease relative to vehicle up to day 25, at which time dosing was discontinued. All treatment arms went on to develop severe disease. Therapeutic administration of Compound 1 was also examined. Treatment began at day 18, by which time all animals had developed severe disease. Compound 1 was administered from day 18 to day 37 and showed to reverse the disease relative to vehicle and was similar to the efficacy observed with fingolimod (i.e., GILENYA® was approved in September 2010 for the treatment of patients with relapsing forms of multiple sclerosis). Similarly, Compound 1 was efficacious in a collagen induced arthritis (CIA) model. Prophylactic oral administration in female Lewis rats resulted in a significant reduction in ankle diameters on day 17 following a daily oral dose and was similar to that observed in rats treated with fingolimod or methotrexate. Improvement in histological parameters in the knees and ankles of CIA rats was also observed, suggesting that inhibiting lymphocyte entry into arthritic joints with Compound 1 treatment suppresses CIA in rodents. Additional details can be found in the following, PCT application, serial number PCT/US2009/004265, filed 22 Jul. 2009 (International Publication Number WO2010/011316); PCT application, serial number PCT/US2011/000153, filed 27 Jan. 2011 (International Publication Number WO2011/094008); and Buzard: D. J., et. al., ACS Med. Chem. Lett. 2014, 5, 1313-1317; each hereby incorporated by reference in its entirety.
The L-arginine salt of Compound 1 was selected for clinical evaluation. A randomized, double-blind, placebo-controlled Phase 1b clinical trial was conducted to evaluate the safety, tolerability, pharmacodynamics, and pharmacokinetics of multiple-ascending doses of the L-arginine salt of Compound 1 in five different dosing cohorts. A total of 50 healthy volunteers received the L-arginine salt of Compound 1 and 10 healthy volunteers received placebo for 21 days. In the Phase 1b clinical trial, the administration of the L-arginine salt of Compound 1 demonstrated a dose-dependent effect on lymphocyte count lowering in blood, with a mean decrease from baseline of up to 69%. Lymphocyte counts, on average, recovered to baseline within one week of the conclusion of dosing.
In view of the growing demand for compounds useful in the treatment of S1P1 receptor-associated disorders, the L-arginine salt of (R)-2-(7-(4-cyclopentyl-3-(trifluoromethyl)benzyloxy)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl)acetic acid (Compound 1) has emerged as an important new compound.
Accordingly, new and efficient methods are needed for the preparation of the L-arginine salt of Compound 1 and crystalline morphologies related thereto. Several improvements have now been discovered in this regard. These improvements are described herein.
Citation of any reference throughout this application is not to be construed as an admission that such reference is prior art to the present application.